The use of dielectric ceramic block filters to remove undesirable electrical frequencies from an electrical signal is well known in the art. Ceramic block filters have found wide acceptance for use in radio communication devices including high frequency devices such as pagers, cellular telephones and other signal processing apparatus.
Traditionally, most external surfaces of the dielectric ceramic block filters are coated with a metallic surface which serves as an electrical ground for the filter. The top and side surfaces of the filter are often used as a printing or patterning surface and often contain a printed metallized pattern which is required in order to achieve the desired frequency response for the filter. However, as the size of the component decreases, printed patterns require a more fine-lined geometry and become increasingly difficult to apply. Another possibility is to chamfer the area around the through-holes on the top or the bottom surfaces of the filter as another method of achieving the desired electrical response. In this instance, a problem can arise as the components become smaller. If the walls around the chamfer become too thin and fragile, large scale manufacturing is not a viable alternative. The significant point, however, is the fact that the processing of the top and/or bottom surfaces of the filter is often an integral step in getting the appropriate electrical filter response.
A trend in the industry is toward components which are smaller in size, require less volume, less weight, and take up less surface area on a printed circuit board, while also keeping a low profile above the surface of the printed circuit board. As such, designers of ceramic block filters are being asked to provide filters with smaller dimensions which exhibit desirable electrical properties. Since the top and bottom surfaces of the ceramic filter are often the surfaces of the block with least surface area, designers are being forced to place intricate electrical patterns and chamfers on a top surface with less and less surface area. Additionally, a shielding structure is also sometimes required in order to protect the filter from stray electromagnetic signals both on the board and emanating from the filter itself. The design and mounting of these shields often results in problems with co-planarity, access to the cells and adhesion among other things.
A ceramic block filter design which provides an increased printing area on the top surface of the ceramic block filter, while allowing many other dimensions of the ceramic block filter to decrease (in response to the demands of the electronics industry), while also providing for some novel shielding configurations, would be considered an improvement over the art.